As is known, vehicle door locks normally comprise a supporting body fixed to a door of the vehicle and a lock mechanism fitted to the supporting body and which engages a striker integral with a door post.
The lock mechanism substantially comprises a fork hinged to the supporting body about a fixed first pin and loaded elastically into a release position, and a latch hinged to the supporting body about a fixed second pin and pushed elastically so that a catch portion of it clicks onto a peripheral edge of the fork.
More specifically, the fork comprises a main body, normally in the form of a metal plate, which defines a C-shaped seat for engaging a normally cylindrical portion of the striker, and comprises two lateral shoulders or teeth which engage the catch portion of the latch. A first tooth is contiguous to the seat, while the second tooth is located on the opposite side of the first tooth to the seat.
A coating, normally of plastic material, covers the main body, so that the teeth project outwards of the coating and, between the two teeth, the coating defines a peripheral guide surface for the catch portion of the latch.
The fork rotates between the release position, in which the seat is oriented to permit insertion and withdrawal of the cylindrical portion of the striker, and a full-lock position, in which the cylindrical portion of the striker engages and is prevented from withdrawing from the seat.
More specifically, in the release position, the fork keeps the catch portion of the latch resting on a peripheral edge portion of the fork located on the opposite side of the second tooth to the first tooth.
The full-lock position of the fork is maintained stably by the catch portion of the latch clicking onto the first tooth of the fork.
In one typical, widely used solution, the fork can also be set to a partial-lock position interposed angularly between the release position and the full-lock position, and in which the cylindrical portion of the striker engages and is prevented from withdrawing from the seat. The partial-lock position of the fork is maintained by the catch portion of the latch engaging the second tooth of the fork. The force by which the cylindrical portion of the striker is retained inside the seat of the fork is obviously greater in the full-lock than in the partial-lock position.
The full-lock position is established when sufficient force is applied to the door to push the striker against the fork forcefully enough to move both teeth past the catch portion of the latch and to arrest the catch portion against the first tooth.
More specifically, as the fork rotates, the peripheral edge of the fork slides on the catch portion of the latch; and, as soon as the second tooth moves past the catch portion, the elastically loaded latch rotates towards the fork, contacts the guide surface at an intermediate point between the two teeth, and eventually clicks onto the first tooth.
The catch portion of the latch contacting the guide surface of the fork produces impact and, therefore, noise. To reduce the noise, the coatings of known forks have, at the intermediate portion of the guide surface portion between the two teeth, a through cavity bounded towards the latch by a flexible edge. When the catch portion of the latch contacts the guide surface, the flexible edge of the cavity therefore flexes inwards of the cavity, and is followed by the guide surface, thus damping impact and reducing noise.
As regards to reducing latch-impact-induced noise, known forks only function satisfactorily when moving into the standard full-lock position. If insufficient force is applied to close the door, the fork may stop in the partial-lock position, thus resulting in non-damped impact and noise.